President Trump’s unilateral pledge Tuesday to end U.S. “war games” with South Korea has emerged as a significant concession in his historic summit with North Korean leader Kim Jong Un, leaving unclear the future of a practice that U.S. officials have long said is important to a decades-old military alliance.

The exercises are held several times each year, focusing on everything from warding off a North Korean attack on its neighbor to the south to “decapitation” strikes aimed at killing key members of the Kim regime. North Korea has traditionally responded to them angrily, while the governments in Seoul and Washington have said they are defensive in nature and part of the “ironclad” U.S.-South Korea alliance designed to ward off North Korean aggression.

Trump seemingly played down the importance of the exercises during a news conference after his summit in Singapore with the North Korean leader, in which Kim broadly agreed to end his nuclear weapons program without providing virtually any specifics on how he would do so. But the president also left open the possibility that the exercises could continue if negotiations don’t work.

“We will stop the war games, which will save us a tremendous amount of money,” Trump said. “Unless and until we see the future negotiation is not going along like it should. We will be saving a tremendous amount of money. Plus, it is very provocative.”

Trump’s use of the term “provocative” marked a notable break with past U.S. policy in itself. The United States has said for years that there is no reason for the Kim regime to see the exercises as inflammatory, including this spring ahead of exercises that had been postponed.

In Singapore, Trump noted that the United States has “done exercises with South Korea for a long time,” but said that it would be “inappropriate” to continue while working out details of the deal.

“We call them war games. I call them war games,” he said. “They are tremendously expensive. The amount of money we spend on that is incredible. South Korea contributes, but not 100 percent, which is a subject that we have to talk to them about also. That has to do with the military expense and also the trade. We actually have a new deal with South Korea. We have to talk to them. We have to talk to countries about treating us fairly. We pay for a big majority of them.”

Trump added in an interview with ABC News that he had questioned what the exercises cost, noting that “we’re flying planes in from Guam, we’re bombing empty mountains for practice.” But he also left open the possibility that they could continue if negotiations falter, saying that he wanted to stop them “unless for some reason we’re unable to go further.”

In a statement, the top U.S. military headquarters in South Korea said Tuesday that it has “received no official updated guidance on execution or cessation on any upcoming training exercises.” Randall Schriver, the Pentagon’s assistant secretary of defense for Asian and Pacific security affairs, was in Singapore for the summit as part of the U.S. delegation, and will return to Washington as the Pentagon considers its next moves.

Dana White, a Pentagon spokeswoman, said Tuesday afternoon in a statement that the Pentagon “welcomes the positive news coming out of the summit” and supports ongoing diplomatic efforts to with North Korea. But she did not address the military exercise issue at all.

“The Presidential summit outcome is the first step along the path to the goal: complete, verifiable and irreversible denuclearization of the Korean Peninsula and a free and open Indo-Pacific,” the statement said.

Abraham Denmark, a deputy assistant secretary of defense for East Asia affairs during the Obama administration, said Tuesday that the United States has previously canceled military exercises with South Korea while attempting to negotiate with its neighbor to the north. During the 1990s, the United States suspended, and later canceled, an exercise known as Team Spirit as they attempted to persuade North Korea to allow inspections of its nuclear facilities.

But Trump calling them “provocative” could be an issue in the future, considering that North Korea and China have traditionally done so, Denmark said.

“I think it’s a characterization that the United States may come to regret if and when we decided to restart joint exercises with South Korea,” Denmark said.

Trump disclosed no cost for the exercises, and the Pentagon did not provide information about the financial considerations. With dozens of aircraft and some ships involved in some of them, the exercises do likely cost millions of dollars, but the operations are part of the Pentagon’s plans to stay prepared for all possibilities, including war. They also could be replaced by other forms of training with similar costs.

The issue was confused further Tuesday afternoon, when Sen. Cory Gardner (R.-Colo.) said that Vice President Pence had told lawmakers on Capitol Hill that regular military training in South Korea would continue. However, he added that formal “war games” would not.

Tom Spoehr, the director of the conservative Heritage Foundation’s Center for National Defense, said in an interview that he wants to hear more about what Trump meant. War games, he said, is “not a term the military uses,” and it’s unclear whether the president was describing large military exercises or broader interactions with the South Koreans.

“If it just means the big and joint exercises, we could do without those for several months. Longer than that, you start to suffer some issues,” said Spoehr, a retired three-star Army general. “You’ve got to train, otherwise you start to get rusty. We can’t go too terribly long without doing these exercises without having some impact.”

It’s also unclear whether Trump was referring to a series of training exercises that forces from the United States, South Korea and Japan carried out over the last year as the Trump administration ramped up its policy of “maximum pressure” on the Kim regime.

On several occasions, aircraft from the three nations flew in formation near the Korean Peninsula, with U.S. and South Korean aircraft then dropping bombs on a training range in South Korea. Photographs of those events were distributed widely by the U.S. military, demonstrating the abilities of the military alliance.

The next major military exercise that had been scheduled between the United States and South Korea was set to begin in August. Last year, that exercise, called Ulchi-Freedom Guardian, involved about 17,500 U.S. troops and focused heavily on computer-simulated exercises.

The most significant exercises are held in the spring. One of them, Foal Eagle, involves field maneuvers, with about 11,500 U.S. troops and 290,000 South Koreans participating. The second, Key Resolve, focuses more on command-and-control preparations, with a heavy reliance on computer simulation and about 12,200 U.S. troops and 10,000 South Koreans involved, the Pentagon said in the spring.